Phenacenes: A family of graphite ribbons. Part 3: Iterative strategies for the synthesis of large phenacenes

Article abstract of DOI:10.1016/S0040-4020(01)00240-X

Iterative strategies are reported for the synthesis of some large monodisperse [n]phenacenes, which are polycyclic aromatic hydrocarbon derivatives having n benzene rings fused in an extended phenanthrene-like structural motif. The key carbon-carbon bond-

Full text of DOI:10.1016/S0040-4020(01)00240-X

TETRAHEDRON
Pergamon
Tetrahedron 57 :2001) 3715±3724
Phenacenes: a family of graphite ribbons. Part 3: Iterative
strategies for the synthesis of large phenacenes
a,p
a
a
a
b
Â
Â
Â
Frank B. Mallory, Kelly E. Butler, Amelie Berube, Eddie D. Luzik, Jr., Clelia W. Mallory,
Emilie J. Brondyke,a Rupa Hiremath,a Phung Ngoa and Patrick J. Carrollb
aDepartment of Chemistry, Bryn Mawr College, Bryn Mawr, PA 19010, USA
bDepartment of Chemistry, University of Pennsylvania, Philadelphia, PA 19104 USA
Received 4 October 2000; accepted 16 January 2001
AbstractÐIterative strategies are reported for the synthesis of some large monodisperse [n]phenacenes, which are polycyclic aromatic
hydrocarbon derivatives having n benzene rings fused in an extended phenanthrene-like structural motif. The key carbon±carbon bond-
forming steps involve either Wittig or McMurry coupling reactions to give diarylethylenes, and oxidative photocyclizations of those
diarylethylenes. tert-Butyl substituents on the phenacene framework serve as solubilizing groups. q 2001 Elsevier Science Ltd. All rights
reserved.
1. Introduction
third dimension :out-of-plane thickness). [n]Phenacenes
with suf®ciently large values of n might be regarded as
psuedo one-dimensional analogs of a single layer of
graphite.
A few years ago we became interested in the synthesis and
properties of some unprecedentedly large polycyclic
aromatic compounds having many fused benzene rings
in an extended zigzag or phenanthrene-like structural
motif.1,2 We have chosen to designate these systems as
[n]phenacenes, where n is the number of fused benzene
rings. Fig. 1 illustrates the concept that [n]phenacenes are
related structurally to a single layer of graphite in the way
that ribbons are related to sheets. Each layer of graphite :i.e.
each graphene sheet) can be regarded as a psuedo two-
dimensional molecule, since two of its dimensions :in-
plane width and length) are each much longer than its
2. Results and discussion
At the time we began our work, [6]phenacene was the
largest member of this family that had been reported; we
quickly added [7]phenacene to this category.1,2 The down-
ward trend in the solubilities of the parent [n]phenacenes
with increasing values of n becomes precipitous around
nˆ6. It was clear that we would need to incorporate
solubilizing groups as ring substituents to make it feasible
to explore the synthesis of larger [n]phenacene systems. We
have investigated several different groups for this purpose;
at present we have settled on using tert-butyl substituents.
From the outset, our general strategy for the construction
of [n]phenacenes has been based on the involvement of
stilbene-like photocyclizations of 1,2-diarylethylene deriva-
tives, a valuable method of wide scope for the synthesis of
phenanthrene-like polycyclic aromatic systems.3 This
photochemical approach is illustrated for the parent stilbene
system in Scheme 1. Upon irradiation with ultraviolet light
in solution, E-stilbene and Z-stilbene interconvert photo-
chemically. In addition, Z-stilbene photocyclizes under
these conditions to give 4a,4b-dihydrophenanthrene as a
transient intermediate. In the absence of a trapping agent,
this intermediate reverts to cis-stilbene by both photo-
chemical and thermal ring-opening reactions, but in the
presence of iodine or oxygen it can be trapped oxidatively
to give phenanthrene.
Figure 1. Representation of a portion of a single layer of graphite :a
graphene sheet) illustrating the concept that [n]phenacene molecules can
be regarded as graphite ribbons.
Keywords: stilbene-like photocyclizations; polycyclic aromatic hydrocar-
bon systems; divergent±convergent syntheses; phenacenes.
p
Corresponding author. Tel.: 11-610-526-5105; fax: 11-610-526-5086;
e-mail: fmallory@brynmawr.edu
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020:01)00240-X

3716
F. B. Mallory et al. / Tetrahedron 57 *2001) 3715±3724
iodine as the trapping agent for the intermediate dihydro-
phenanthrene derivative gave the substituted phenanthrene
hν
H
6. The overall yield of the ®ve-step synthesis of 6 from 1
was 54%. The methyl and bromo functionality that was
hν
³
H
∆
present in starting material 1 is once again present in the
product of the ®rst iteration, 6, which allows a second itera-
tion to be carried out in an analogous way. As outlined in
Scheme 2, phenanthrene 6 was transformed by way of
bromomethyl compound 7, phosphonium salt 8, aldehyde
9, and stilbene analog 10 to produce the [7]phenacene
hν
hν
I2 (or O2)
³
derivative 11 in an overall yield of 47% for the second
iteration.
+ 2 HI (or H2O2)
Scheme 1.
Our divergent±convergent iterative strategy seems espe-
cially well suited, in principle, for the synthesis of very
large [n]phenacenes because the number of fused rings
formed, n, is related exponentially to the number of iter-
ations carried out, I; the actual relationship is nˆ2:I11)21.
Looking ahead optimistically beyond the two completed
iterations outlined in Scheme 2, one can see that two
additional iterations, if successful, would transform the
[7]phenacene derivative 11 into the corresponding
[15]phenacene and [31]phenacene derivatives, respectively.
We are pursuing three different approaches to the synthesis
of large [n]phenacenes, each involving iterative elongation
of smaller [n]phenacenes. These different approaches
employ similar strategies in the assembly process for the
construction of the new carbon±carbon bonds. First
the double bond of a diarylethylene is formed, either by
Wittig coupling of an aryl aldehyde with an ylid derived
from a benzylic triphenylphosphonium salt, or by McMurry
coupling of an aryl aldehyde, and then the diarylethylene is
photocyclized to form another carbon±carbon bond. In this
chemistry we employ either bromo or methyl groups as
latent aldehydes, and methyl groups as latent ylids.
2.2. Synthesis of symmetrical phenacenes by double
photocyclizations
The other iterative approach we are investigating for
the synthesis of large [n]phenacenes is a versatile method
involving the double photocyclizations of the bis-stilbene
derivatives that are produced by Wittig reactions of benzylic
phosphonium salts with an appropriate centerpiece aromatic
dialdehyde. This bis-stilbene approach necessarily produces
symmetrically substituted phenacenes, in contrast with the
2n11 approach, which produces unsymmetrically sub-
stituted phenacenes as noted above. Scheme 3 illustrates
one example of this bis-stilbene approach. We refer to this
particular example as the n18 method, because each inter-
ation transforms a phenacene system having n fused ben-
zene rings into a new phenacene system having n18 fused
benzene rings. Treatment of bromomethyl compound 2
:Scheme 2) with the anion derived by deprotonation of
2-nitropropane gave aldehyde 12. The coupling reaction
of 12 using titanium tetrachloride and zinc gave stilbene
derivative 13, and the photocyclization of 13 gave the
symmetrical dibromophenanthrene 14, which can be
2.1. Synthesis of unsymmetrical phenacenes
One of our iterative approaches involves a divergent±
convergent4 strategy, as illustrated in Scheme 2. This
approach leads to the synthesis of unsymmetrically sub-
stituted phenacenes having bromo functionality on one
terminal ring and methyl functionality on the other terminal
ring. We refer to this as the 2n11 method, because each
iteration converts a system with n benzene rings into a new
system with 2n11 benzene rings. The starting material for
the ®rst iteration is 2-bromo-4-tert-butyltoluene :1), a
compound that is readily prepared on a large scale by the
reaction of commercially available 4-tert-butyltoluene with
bromine in acetic acid.5 Treatment of 1 with N-bromo-
succinimide in carbon tetrachloride gave benzylic bromide
2, and subsequent treatment of 2 with triphenylphosphine in
acetone gave the corresponding benzylic phosphonium salt
3. In a parallel reaction, lithium±bromine exchange of 1
using n-butyllithium in a mixture of hexane and THF,
followed by treatment of the resulting aryllithium derivative
with N,N-dimethylformamide, gave aldehyde 4. A phase-
transfer Wittig reaction in which 50% aqueous sodium
hydroxide was added to a solution of phosphonium salt 3
³
To calculate the overall percentage yield for the conversion of 1 to 6 in the
®rst iteration of this divergent±convergent method, one can imagine that
1.00 equiv. of 1 is divided into two portions of 0.55 and 0.45 equiv.,
respectively. Hypothetically, the 0.55 equiv. portion of 1 could be used
to produce :in two steps with yields of 92 and 85%) 0.43 equiv. of phos-
phonium salt 3, and the 0.45 equiv. portion could be used to produce :in
one step with a yield of 97%) 0.43 equiv. of aldehyde 4. Hypothetically,
the subsequent Wittig reaction :73% yield) of 0.43 equiv. of 3 and
0.43 equiv. of 4 would give 0.31 equiv. of stilbene 5, which would
undergo photocyclization :88% yield) to give 0.27 equiv. of phenanthrene
6. Note that if each step in this ®ve-step ®rst iteration took place in 100%
yield, the overall theoretical yield from 1.00 equiv. of 1 would be only
0.50 equiv. of 6. Therefore our overall experimental percentage yield of 6
is 0.27/0.50ˆ54%. The overall experimental percentage yield for the
conversion of 6 to 11 in the second ®ve-step iteration can be calculated
analogously to be 47% by imagining that 0.51 equiv. of 6 is used to
synthesize phosphonium salt 8 and 0.49 equiv. of 6 is used to synthesize
aldehyde 9. The overall yields of 54 and 47%, respectively, for the ®rst
two iterations give a combined overall yield for the two iterations of 25%.
²
and aldehyde 4 in CH2Cl2 produced stilbene derivative 5.
To complete the ®rst iteration, oxidative photocyclization of
5 by ultraviolet irradiation in hexane solution containing
²
The Wittig reactions reported herein produced the diarylethylenes as
mixtures of E and Z isomers. For purposes of puri®cation and character-
ization, solutions of these isomer mixtures containing small amounts of I2
were irradiated with visible light from a 100 W tungsten bulb to generate
iodine atoms by the photolysis of I2. The resulting iodine atoms catalyzed
the thermal Z-to-E isomerizations of the diarylethylenes to produce the
thermodynamically favored Eisomers. These :E)-diarylethylenes served
as the starting materials for the subsequent ultraviolet photocyclizations
:see Scheme 1).

F. B. Mallory et al. / Tetrahedron 57 *2001) 3715±3724
3717
Br
CHO
TiCl4
Br
Br
Br
CH3
Me2CHNO2
2
EtONa
88%
Zn
NBS
92%
1. n-BuLi
12
13
97%
t-Bu
t-Bu
t-Bu
1
t-Bu
2. DMF
97%
2
hν, I2
58%
Br
Br
Ph3P
85%
Br–
Ph3P
Br
14
t-Bu
t-Bu
61%
CH2
OHC
CH3
Wittig
73%
1. n-BuLi
2. DMF
3
t-Bu
4
t-Bu
OHC
CHO
Br
CH3
t-Bu
t-Bu
15
5
Br–
Br–
t-Bu
t-Bu
Ph3P
PPh3
88%
Br
CH2
H2C
Br
hν, I2
Wittig
58%
Br
CH3
8
8
t-Bu
t-Bu
t-Bu
t-Bu
NBS
94%
1. n-BuLi
Br
Br
t-Bu
t-Bu
6
2. DMF
86%
7
Ph3P
87%
t-Bu
t-Bu
t-Bu
t-Bu
43%
t-Bu
t-Bu
t-Bu
16
Br–
Ph3P
hν, I2
Br
CH2
OHC
CH3
Wittig
14
11
8
5
Br
Br
8
t-Bu
9
89%
t-Bu
Br
t-Bu
t-Bu
CH3
17
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
Scheme 3.
10
t-Bu
t-Bu
t-Bu
t-Bu
[11]phenacene derivative 17 sequentially into the corre-
sponding [19]phenacene and [27]phenacene derivatives,
respectively. Although the number of fused rings produced
in the n18 approach depends only linearly on the number
of iterations accomplished, this approach nevertheless is
quite ef®cient as a method for the synthesis of moderately
large phenacenes.
63%
hν, I2
9
6
Br
12
CH3
3
t-Bu
t-Bu
t-Bu
t-Bu
11
2.3. Synthesis of symmetrical phenacenes by single
photocyclizations
Scheme 2.
regarded as the starting material for the ®rst iteration of this
n18 method. Treatment of 14 with n-butyllithium followed
by N,N-dimethylformamide gave the dialdehyde center-
piece 15, which was then subjected to a Wittig reaction
with 2 equiv. of the phosphonium salt 8 :Scheme 2)
to give bis-stilbene 16. To complete the ®rst iteration,
bis-stilbene 16 was doubly photocyclized to give the
dibromo[11]phenacene derivative 17. The strategic concept
of this n18 method is that the dibromophenacene product of
each iteration should be capable, in principle, of reacting
with n-butyllithium and N,N-dimethylformamide to give a
new dialdehyde that might serve as the centerpiece for a
As an alternative to the centerpiece method for the synthesis
of symmetrically substituted phenacenes by double photo-
cyclizations of bis-stilbenes, we have developed a method
that involves single photocyclizations of mono-stilbenes.
This alternative method starts with an unsymmetrically
substituted phenacene with n fused benzene rings and meth-
yl and bromo substituents, respectively, on the two terminal
rings, and transforms it into a symmetrically substituted
phenacene with 2n11 fused rings and bromo substituents
on each of the terminal rings. As shown in Scheme 4, for
example, the [3]phenacene derivative 6 :Scheme 2) was
subjected to benzylic bromination to give 7 :Scheme 2),
and treatment of 7 with 2-nitropropane and sodium
ethoxide gave aldehyde 18. Coupling of 18 using titanium
tetrachloride and zinc gave the symmetrical diarylethylene
subsequent iteration involving phosphonium salt
:Scheme 2). For example, two additional iterations of
8
this n18 method, if successful, would transform the

3718
F. B. Mallory et al. / Tetrahedron 57 *2001) 3715±3724
CHO
Br
material was shown to be identical with the sample of 17
that had been synthesized by the centerpiece strategy
outlined in Scheme 3, which provides additional support
for our assignment of the structure of this compound.
NBS
94%
Me2CHNO2
6
7
EtONa
99%
18
t-Bu
t-Bu
t-Bu
t-Bu
Br
Br
2.4. Deviations from planarity of the polycyclic carbon
frameworks of phenacenes
TiCl4
Zn
78%
19
Our decision to use tert-butyl groups as solubilizing sub-
stituents was made in part because the reactions we are
employing to assemble larger phenacenes from smaller
ones are not compatible with the presence of any benzylic
hydrogens other than those on the single methyl substituent
whose chemical manipulation we are relying upon in our
synthetic strategies. Because these tert-butyl groups are
attached in the bay regions of our phenacenes, they experi-
ence signi®cant intramolecular crowding with the hydrogen
atoms at the opposite bay positions. As a consequence of
these destabilizing steric interactions, each tert-butyl group
would be expected to be forced up :or down) out of the
rough local plane of the carbon framework of the polycyclic
aromatic system in its immediate vicinity. One might
consider a priori two limiting cases of cooperativity for
the way in which the relief of this local steric crowding
might manifest itself in the shape of the framework of the
aromatic ring carbons for an extended phenacene derivative.
First, if a given tert-butyl group is forced out of the rough
plane of the ring carbon atoms in its immediate vicinity in
one direction :e.g. `up'), it might be that the adjacent tert-
butyl group would experience this distortion in the opposite
direction :e.g. `down') as shown in Fig. 2:a). Alternatively,
each of the tert-butyl groups might distort in same direction
:all up or all down) as shown in Fig. 2:b). In the ®rst case,
the polycyclic framework of carbon atoms would be twisted
out of its average plane alternatively in a clockwise sense
and then in a counterbalancing counterclockwise sense
along the path from one end of the phenacene to the other,
with the end result that the two terminal rings might lie
approximately in the same plane. In the second case, it
would be expected that the `plane' of the polycyclic frame-
work of ring carbon atoms would twist continuously around
the long dimension of the framework in a helical sense
:either right-handed or left-handed) from one end of the
phenacene to the other. We have succeeded in growing a
crystal of the unsymmetrical [7]phenacene derivative 11
that was suitable for single-crystal X-ray analysis. As
shown in Fig. 3, the results of that analysis show that at
t-Bu
t-Bu
t-Bu
Br
Br
hν, I2
82%
20
t-Bu
t-Bu
t-Bu
Scheme 4.
19, which in turn was photocyclized to give the symmetri-
cally substituted dibromo[7]phenacene derivative 20.
Another example of this strategy is shown in Scheme 5. This
particular example also illustrates how phosphonium salts
and aldehydes of different sizes can be used to construct a
diverse set of building blocks for the synthesis of large
phenacenes. Wittig coupling of phosphonium salt 8 and
aldehyde 4 :both from Scheme 2) gave diarylethylene 21,
and the photocyclization of 21 gave the [5]phenacene
derivative 22. Functionalization of the ring methyl group
in 22 by benzylic bromination gave 23, which was then
transformed to aldehyde 24. Coupling of 24 gave the
symmetrical diarylethylene 25, and photocyclization of 25
gave the dibromo[11]phenacene derivative 17. This
Br–
Ph3P
Br
CH2
OHC
CH3
Wittig
64%
21
8
4
t-Bu
t-Bu
Br
t-Bu
CH3
NBS
87%
hν, I2
50%
t-Bu
t-Bu
t-Bu
22
Br
CHO
24
Me2CHNO2
23
EtONa
54%
t-Bu
t-Bu
t-Bu
Br
CH3
TiCl4, Zn
44%
(a)
(b)
Br
Br
t-Bu
t-Bu
t-Bu
t-Bu
Br
CH3
t-Bu
t-Bu
t-Bu
t-Bu
hν, I2
25 t-Bu
t-Bu
t-Bu
t-Bu
73%
Br
Br
t-Bu
t-Bu
t-Bu
t-Bu
Figure 2. Structures of two hypothetical limiting possibilities for the stereo-
chemical disposition of the tert-butyl substituents in the [7]phenacene deri-
vative 11: :a) with the tert-butyl groups arrayed in a syndiotactic sense, and
:b) with the tert-butyl groups arrayed in an isotactic sense.
t-Bu
t-Bu
17 t-Bu
t-Bu
Scheme 5.

F. B. Mallory et al. / Tetrahedron 57 *2001) 3715±3724
3719
to room temperature, water and aqueous sodium bisul®te
were added, and the product was extracted with ether. The
combined extracts were washed with water, dried with
sodium sulfate, and ®ltered. Rotary evaporation of the
®ltrate gave a yellow liquid that was distilled :78±828C,
0.03 mm Hg) to give 67.4 g :88%) of 1 as a pale yellow
1
liquid: HNMR d 7.56 :d, Jˆ1.8 Hz, 1H; H-3), 7.25 :dd,
Jˆ8.0, 1.8 Hz, 1H; H-5), 7.18 :d, Jˆ8.0 Hz, 1H; H-6), 2.39
:s, 3H; ring CH3), 1.32 :s, 9H; :CH3)3C); 13C NMR d
150.94, 134.86, 130.60, 129.51, 125.02, 124.51, 34.59,
31.45, 22.53. Anal. Calcd for C11H15Br: C, 58.17; H, 6.66.
Found: C, 58.30; H, 6.69.
Figure 3. An ORTEP representation of the molecular structure of the
[7]phenacene derivative 11 as determined by single crystal X-ray analysis.
This edge-on view, with the rough plane of the polycyclic aromatic frame-
work approximately perpendicular to the page, illustrates the syndiotactic
disposition of the tert-butyl substituents.
4.1.2. 2-Bromo-4-tert-butylbenzyl bromide 12). A mag-
netically stirred mixture of 18.7 g :105 mmol) of N-bromo-
succinimide, 23.8 g :105 mmol) of 1, a pinch of benzoyl
peroxide, and 150 mL of carbon tetrachloride was heated
under re¯ux overnight. The reaction mixture was allowed to
cool and then the succinimide was removed by ®ltration.
The ®ltrate was rotary evaporated and the residue was
distilled :104±1228C, 0.04 mm Hg) to give 29.6 g :92%)
of 2 as a clear, colorless liquid: 1HNMR d 7.57 :d,
Jˆ1.9 Hz, 1H; H-3), 7.38 :d, Jˆ8.1 Hz, 1H; H-6), 7.30
:dd, Jˆ8.1, 1.9 Hz, 1H; H-5), 4.59 :s, 2H; CH2Br), 1.29
:s, 9H; :CH3)3C); 13C NMR d 153.83, 133.84, 130.81,
130.32, 125.05, 124.31, 34.67, 33.34, 31.03. Anal. Calcd
for C11H14Br2: C, 43.17; H, 4.61. Found: C, 42.91; H, 4.89.
least for this particular phenacene the tert-butyl substituents
alternate up and down.
3. Conclusions
A long-term objective of our work is to synthesize [n]phena-
cenes with dramatically large values of n in the hope that
these compounds might possess properties that could make
them potentially interesting and useful as materials. In the
shorter term, our objective is to produce a family of well-
characterized monodisperse [n]phenacenes with different
values of n to permit the systematic determination of trends
in various properties of these compounds as a function of n.
In this way, we hope to gain some fundamental insights
about the structural and electronic properties of long conju-
gated p systems.
4.1.3. 2-Methyl-5-tert-butylbenzaldehyde 14). A mag-
netically stirred solution of 15.6 g :69 mmol) of 1 in
400 mL of anhydrous ether was cooled in an ice bath
under nitrogen. After the dropwise addition of 55 mL
:138 mmol) of a 2.5 M solution of n-BuLi in hexanes, the
reaction mixture was stirred for an additional 30 min, and
then 14 mL :180 mmol) of DMF was added dropwise. The
reaction mixture was allowed to warm to room temperature,
and then was poured into dilute aqueous phosphoric acid.
The product was extracted with ether, and the combined
extracts were washed with sodium bicarbonate and water,
dried with sodium sulfate, and ®ltered. The ®ltrate was
rotary evaporated and the yellow liquid residue was chro-
matographed on silica gel with 5% ethyl acetate in hexanes
as eluent to give 11.8 g :97%) of 4 as a pale yellow liquid:
bp 70±858C :0.03 mm Hg); 1HNMR d 10.28 :s, 1H; CHO),
7.82 :d, Jˆ2.2 Hz, 1H; H-6), 7.52 :dd, Jˆ8.0, 2.2 Hz, 1H;
H-4), 7.20 :d, Jˆ7.7 Hz, 1H; H-3), 2.63 :s, 3H; ring CH3),
1.34 :s, 9H; :CH3)3C); 13C NMR d 193.03, 149.42, 137.76,
133.83, 131.71, 130.95, 128.65, 34.52, 31.26, 18.99. Anal.
Calcd for C12H16O: C, 81.88; H, 9.10. Found: C, 81.75; H,
8.92.
4. Experimental
4.1. General
Melting points were determined with an oil-bath apparatus
1
and are uncorrected. HNMR spectra were measured at
300 MHz and 13C NMR spectra were measured at 75 MHz
in CDCl3 solution at ambient temperature unless otherwise
speci®ed. All chemical shifts :d) have been referenced to
tetramethylsilane as an internal standard. For some
1
compounds of relatively low solubility, HNMR spectra
were measured in 1,4-dichlorobenzene-d4 solution at
temperatures $558C; the singlet signal from the incom-
pletely deuteriated solvent molecules at 7.03 ppm relative
to internal TMS was used as a secondary reference standard
in the spectra obtained at these elevated temperatures.
Photocyclizations were carried out in magnetically stirred
hydrocarbon solutions in quartz vessels in a Rayonet reactor
equipped with a set of 16 300 nm lamps. Elemental analyses
were performed by M-H-W Laboratories, P.O. Box 15149,
Phoenix, AZ 85018.
4.1.4. 1E)-2-Bromo-4,50-di-tert-butyl-20-methylstilbene
15). A magnetically stirred solution of 7.7 g :25 mmol) of
benzylic bromide 2 and 7.9 g :30 mmol) of triphenyl-
phosphine in 100 mL of xylenes was heated under re¯ux
overnight. The reaction mixture was cooled to room
temperature. A beige solid was collected by vacuum ®ltra-
tion, washed with toluene, and dried in an oven at 758C to
give 12.2 g :85%) of the benzylic phosphonium salt 3.
4.1.1. 2-Bromo-4-tert-butyltoluene 11). A previously
reported method was used.5 Following the slow addition
of 21 mL :406 mmol) of bromine to a solution of 50 g
:338 mmol) of 4-tert-butyltoluene in 150 mL of glacial
acetic acid at room temperature, the solution was heated
at 508C for 5 d. The reaction mixture was allowed to cool
Phosphonium salt 3 :12.2 g, 21.5 mmol) was placed in 30 mL
of methylene chloride along with 4.54 g :25.8 mmol) of alde-
hyde 4. Then 10 mL of 50% aqueous sodium hydroxide was

3720
F. B. Mallory et al. / Tetrahedron 57 *2001) 3715±3724
added slowly and the vigorously stirred mixture was heated
under re¯ux for 1 h. The layers were separated and the
aqueous layer was washed with ether. The combined
organic extracts were washed with water, dried with sodium
sulfate, and ®ltered. The ®ltrate was rotary evaporated
and 300 mL of cyclohexane was added to the residue. The
insoluble triphenylphosphine oxide was removed by ®ltra-
tion. The ®ltrate was washed with 70% aqueous ethanol to
remove residual triphenylphosphine oxide, dried over
sodium sulfate, and ®ltered. A crystal of iodine was added
to the ®ltrate, and the magnetically stirred solution was
irradiated with visible light for 3 days to effect Z-to-E
isomerization. The solution was washed with aqueous
sodium bisul®te and the organic layer was rotary evapo-
rated. The yellow liquid residue was puri®ed by column
chromatography on silica gel with hexanes as eluent to
give 6.0 g :73%) of 5 as a clear, colorless liquid that spon-
taneously crystallized and subsequently was recrystallized
:d, Jˆ9.3 Hz, 1H; H-10), 7.97 :d, Jˆ9.3 Hz, 1H; H-9),
7.85 :d, Jˆ1.8 Hz, 1H; H-2), 7.81 :d, Jˆ7.9 Hz, 1H; H-6),
7.53 :d, Jˆ7.9 Hz, 1H; H-7), 4.92 :s, 2H; CH2Br), 1.52 :s,
9H; :CH3)3C), 1.42 :s, 9H; :CH3)3C); 13C NMR d 150.20,
146.3, 132.62, 132.24, 131.29, 130.45, 129.96, 129.88,
129.61, 129.17, 127.27, 124.87, 122.90, 121.85, 39.46,
35.28, 34.09, 31.66, 31.38. Anal. Calcd for C23H26Br2: C,
59.76; H, 5.67. Found: C, 59.90; H, 5.53.
4.1.7. 3,5-Di-tert-butyl-8-methylphenanthrene-1-carbox-
aldehyde 19). A procedure similar to that described above
for aldehyde 4 was followed. Starting from 4.88 g
:12.7 mmol) of bromophenanthrene 6, 40 mL of anhydrous
ether, 8.6 mL :19.1 mmol) of a 2.0 M solution of n-BuLi in
pentane, and 2.0 mL :25.8 mmol) of DMF there was
obtained, after recrystallization of the crude product from
acetonitrile, 3.61 g :86%) of 9 as yellow crystals: mp
1
113.5±114.08C; HNMR d 10.54 :s, 1H; CHO), 8.91 :d,
1
to constant mp from hexanes: mp 81.5±82.58C; HNMR
Jˆ9.3 Hz, 1H; H-10), 8.53 :d, Jˆ1.9 Hz, 1H; H-4), 8.07 :d,
Jˆ2.1 Hz, 1H; H-2), 7.95 :d, Jˆ9.3 Hz, 1H; H-9), 7.81 :d,
Jˆ7.8 Hz, 1H; H-6), 7.37 :d, Jˆ7.9 Hz, 1H; H-7), 2.68 :s,
3H; ring CH3), 1.53 :s, 9H; :CH3)3C), 1.48 :s, 9H; :CH3)3C);
13C d 193.92, 146.20. 134.93, 132.46, 132.01, 131.90,
131.48, 130.04, 129.20, 128.86, 127.17, 125.68, 120.75,
38.10, 35.29, 34.48, 31.55, 19.38. Anal. Calcd for
C24H28O: C, 86.70; H, 8.49. Found: C, 86.89; H, 8.33.
:assignments established by homonuclear decoupling) d
7.62 :d, Jˆ2.0 Hz, 1H; H-60), 7.60 :d, Jˆ8.8 Hz, 1H; H-
6), 7.59 :d, Jˆ1.8 Hz, 1H; H-3), 7.34 :dd, Jˆ8.0, 2.1 Hz,
1H; H-5), 7.29 :A of AB q, Jˆ15.9 Hz, 1H; H-a or H-a0).
7.22 :B of AB q, Jˆ15.9 Hz, 1H; H-a0 or H-a), 7.25 :dd,
Jˆ7.9, 2.1 Hz, 1H; H-40), 7.13 :d, Jˆ8.0 Hz, 1H; H-30),
2.39 :s, 3H; ring CH3), 1.36 :s, 9H; 50-:CH3)3C), 1.32 :s,
9H; 4-:CH3)3C); 13C NMR d 152.37, 149.02, 135.77,
134.74, 133.01, 130.20, 129.95, 129.33, 128.47, 126.48,
124.99, 124.78, 124.02, 122.74, 34.64, 34.43, 31.39,
31.13, 19.44. Anal. Calcd for C23H29Br: C, 71.87; H, 7.34.
Found: C, 71.63; H, 7.60.
4.1.8. 1E)-1-18-Bromo-4,6-di-tert-butyl-1-phenanthryl)-
2-180-methyl-30,50-di-tert-butyl-10-phenanthryl)ethene
110). A procedure similar to that described above for phos-
phonium salt 3 was followed to convert 22.9 g :49.4 mmol)
of benzylic bromide 7 and 13.0 g :49.4 mmol) of triphenyl-
phosphine in 150 mL of xylenes to 31.2 g :87%) of the
corresponding phosphonium salt 8 as a beige solid.
4.1.5. 1-Bromo-3,5-di-tert-butyl-8-methylphenanthrene
16). A solution of 2.5 g :6.5 mmol) of stilbene 5 and 0.8 g
:3.1 mmol) of iodine in 1.0 L of hexanes was irradiated
:Rayonet) for 3 d at 10±208C. After the reaction mixture
was concentrated to about 100 mL by rotary evaporation,
it was washed with aqueous sodium bisul®te. The organic
layer was dried over sodium sulfate and ®ltered. The ®ltrate
was passed through a short pad of silica gel and then was
rotary evaporated. The oily residue was triturated with
acetonitrile to yield 2.2 g :88%) of 6 as colorless crystals:
A sample of 1.58 g :39.6 mmol) of sodium hydride :60%
dispersion in mineral oil) was washed twice with hexanes
and then was heated with 40 mL of DMSO at 60±808C until
the evolution of gas ceased. This solution was cooled to
room temperature, and a slurry of 25.4 g :35.1 mmol) of
phosphonium salt 8 in 100 mL of DMSO was added. The
reaction mixture turned red, indicating the formation of the
ylid. Then a slurry of 11.6 g :34.8 mmol) of aldehyde 9 in
100 mL of DMSO was added, and the mixture was heated to
808C for 3.5 h until all of the red color disappeared. The
cloudy yellow solution was cooled in an ice bath and ®ltered
to give a yellow solid that was washed with methanol and
dried under vacuum to yield 21.5 g :89%) of a mixture of
diarylethylene 10 and its Z isomer. This material, along with
a crystal of iodine, was dissolved in cyclohexane, and the
magnetically stirred solution was irradiated with visible
light for 2 d. The solution was washed with aqueous sodium
bisul®te and the organic layer was dried with sodium sulfate
and ®ltered. The ®ltrate was rotary evaporated and the resi-
due was recrystallized from a mixture of toluene and 95%
ethanol to give 10 as white crystals: mp 253.5±254.58C; 1H
NMR d 8.28 :d, Jˆ1.5 Hz, 1H; H-5 or H-40), 8.25 :d,
Jˆ1.4 Hz, 1H; H-40 or H-5), 8.11 :A of AB q, Jˆ9.4 Hz,
1H; H-9 or H-10), 8.04 :B of AB q, Jˆ9.4 Hz, 1H; H-10 or
H-9), 8.04 :d, Jˆ9.5 Hz, 1H; H-100), 7.95 :A of AB q,
Jˆ8.1 Hz, 1H; H-2 or H-3), 7.90 :B of AB q, Jˆ8.1 Hz,
1H; H-3 or H-2), 7.89 :d, Jˆ1.7 Hz, 1H; H-7 or H-20),
7.88 :d, Jˆ1.6 Hz, 1H; H-7 or H-20), ca. 7.86 and 7.84
1
mp 140.6±141.08C; HNMR d 8.24 :d, Jˆ1.4 Hz, 1H;
H-4), 8.03 :d, Jˆ9.2 Hz, 1H; H-10), 7.83 :d, Jˆ9.2 Hz,
1H; H-9), 7.83 :d, Jˆ1.8 Hz, 1H; H-2), 7.77 :d, Jˆ7.8 Hz,
1H; H-6), 7.34 :d, Jˆ7.8 Hz, 1H; H-7), 2.65 :s, 3H; ring
CH3), 1.53 :s, 9H; :CH3)3C), 1.42 :s, 9H; :CH3)3C); 13C
NMR d 147.12, 146.54, 133.62, 132.88, 132.44, 132.28,
129.67, 129.27, 129.14, 129.07, 127.72, 124.72, 124.48,
122.43, 38.20, 35.46, 34.44, 31.62, 19.26; UV :benzene,
nm [e]) 324 [13,000], 314 [14,000], 286 [27,000]. Anal.
Calcd for C23H27Br: C, 72.06; H, 7.05. Found: C, 71.98;
H, 7.27.
4.1.6. 1-Bromo-3,5-di-tert-butyl-8-bromomethylphenan-
threne 17). A procedure similar to that described above
for benzylic bromide 2 was followed. A mixture of 5.11 g
:28.7 mmol) of N-bromosuccinimide, 11.0 g :28.7 mmol) of
methylphenanthrene 6, a pinch of benzoyl peroxide, and
90 mL of carbon tetrachloride was heated under re¯ux for
48 h. Recrystallization of the crude product from hexanes
yielded 12.5 g :94%) of 7 as a beige solid: mp 142.5±
1
143.58C; HNMR d 8.20 :d, Jˆ1.2 Hz, 1H; H-4), 8.14

F. B. Mallory et al. / Tetrahedron 57 *2001) 3715±3724
3721
1
:presumably AB q with outer lines too weak to observe, 2H;
H-a and H-a0), 7.78 :d, Jˆ9.0 Hz, 1H; H-90), 7.78 :d, Jˆca.
8 Hz, 1H; H-60), 7.34 :d, Jˆ7.8 Hz, 1H; H-70), 2.66 :s, 3H;
ring CH3), 1.58 :s, 18H; :CH3)3C), 1.50 :s, 9H; :CH3)3C),
1.45 :s, 9H; :CH3)3C); 13C NMR d 148.30, 146.17, 145.92,
144.42, 133.46, 133.01, 132.67, 132.03, 131.96, 131.87,
131.37, 131.05, 130.62, 129.01, 128.94, 128.60, 128.45,
128.34, 128.27, 128.17, 126.45, 124.02, 123.91, 123.76,
122.60, 122.23, 121.68, 121.32, 38.28, 38.00, 35.24,
34.31, 34.18, 31.61, 31.43, 19.29. Anal. Calcd for
C47H53Br: C, 80.89; H, 7.66. Found: C, 80.96; H, 7.58.
as a light yellow oil: HNMR d 10.33 :s, 1H; CHO), 7.87
:d, Jˆ8.2 Hz, 1H; H-6), 7.65 :d, Jˆ1.6 Hz, 1H; H-3), 7.45
:dd, Jˆ8.2, 1.4 Hz, 1H; H-5), 1.35 :s, 9H; :CH3)3C); 13C
NMR d 191.37, 159.78, 131.12, 130.88, 129.60, 127.28,
125.23, 35.40, 30.90. Anal. Calcd for C11H13BrO: C,
54.79; H, 5.43. Found: C, 54.60; H, 5.19.
4.1.11. 1E)-2,20-Dibromo-4,40-di-tert-butylstilbene 113).
To
a magnetically stirred yellow slurry of 3.69 g
:19.4 mmol) of titanium tetrachloride in 75 mL of THF
that was cooled in an ice bath under nitrogen was added
2.32 g :35.3 mmol) of zinc dust. Then 4.26 g :17.7 mmol)
of aldehyde 12 was added, and the mixture was heated under
re¯ux for 4 h. The cooled reaction mixture was poured into
dilute aqueous hydrochloric acid, and the product was
extracted with hexanes. The combined extracts were washed
with water and brine, dried with sodium sulfate, and ®ltered.
The ®ltrate was rotary evaporated to give 3.86 g :97%) of 13
as a light-beige powder, which was recrystallized from a
mixture of toluene and 95% ethanol to give 13 as white
4.1.9. 11-Bromo-4-methyl-1,13,15,17-tetra-tert-butyl[7]
phenacene 111). A suspension of 4.05 g :5.8 mmol) of
stilbene 10 and 1.6 g :6.3 mmol) of iodine in 60 mL of
toluene and 1 L of distilled hexanes was irradiated
:Rayonet) for 60 h. Rotary evaporation of the reaction
mixture and recrystallization of the residue from a mixture
of toluene and 95% ethanol gave 2.54 g :63%) of 11 as a
pale yellow powder: mp 3788C :dec); HNMR :CDCl ) d
1
3
1
8.88 :A of AB q, Jˆ9.3 Hz, 1H; H-7 or H-8), 8.74 :B of AB
q, Jˆ9.3 Hz, 1H; H-8 or H-7), 8.84 :s, 1H; H-16 or H-18),
8.79 :d, Jˆ9.4 Hz, 1H; H-9), 8.75 :s, 1H; H-18 or H-16),
8.60 :d, Jˆ9.3 Hz, 1H; H-6), 8.45 :d, Jˆ1.3 Hz, 1H; H-14),
8.32 :d, Jˆ9.2 Hz, 1H; H-10), 8.08 :d, Jˆ9.2 Hz, 1H; H-5),
7.92 :d, Jˆ1.7 Hz, 1H; H-12), 7.86 :d, Jˆ7.8 Hz, 1H; H-2),
7.42 :d, Jˆ8.1 Hz, 1H; H-3), 2.78 :s, 3H; ring CH3), 1.65 :s,
9H; :CH3)3C), 1.57 :s, 18H; :CH3)3C), 1.51 :s, 9H;
needles: mp 126±1278C; HNMR d 7.65 :d, Jˆ8.3 Hz,
2H; H-6,60), 7.58 :d, Jˆ1.9 Hz, 2H; H-3,30), 7.35 :dd,
Jˆ8.1, 2.0 Hz, 2H; H-5,50), 7.34 :s, 2H; H-a,a0), 1.32 :s,
18H; :CH3)3C); 13C NMR d 153.22, 134.48, 130.40, 129.62,
127.05, 125.32, 124.57, 35.13, 31.54. Anal. Calcd for
C22H26Br2: C, 58.69; H, 5.82. Found: C, 58.80; H, 5.70.
4.1.12. 1,8-Dibromo-3,6-di-tert-butylphenanthrene 114).
A solution of 2.36 g :5.24 mmol) of stilbene 13 and 0.67 g
:2.64 mmol) of iodine in 1 L of cyclohexane was irradiated
:Rayonet) for 11 h. The reaction mixture was rotary evapo-
rated and the dark solid residue was dissolved in a mixture
of hexanes and toluene and ®ltered through alumina. The
®ltrate was rotary evaporated and the crystalline residue was
recrystallized from a mixture of 95% ethanol and hexanes to
give 1.36 g :58%) of 14 as a white needles: mp 131.5±
1
:CH3)3C); HNMR :1,4-dichlorobenzene- d4, 608C) 8.94
:s, 1H; H-16 or H-18), 8.82 :s, 1H; H-18 or H-16), 8.77
:A of AB q, Jˆ9.3 Hz, 1H; H-7 or H-8), 8.64 :B of AB q,
Jˆ9.3 Hz, 1H; H-8 or H-7), 8.69 :d, Jˆ9.2 Hz, 1H; H-9),
8.51 :br s, 1H; H-14), 8.46 :d, Jˆ9.2 Hz, 1H; H-6), 8.30 :d,
Jˆ9.2 Hz, 1H; H-10), 7.94 :d, Jˆ9.2 Hz, 1H; H-5), 7.91 :d,
Jˆ1.7 Hz, 1H; H-12), 7.40 :d, Jˆ7.7 Hz, 1H; H-2), 7.28 :d,
Jˆ7.8 Hz, 1H; H-3), 2.64 :s, 3H; ring CH3), 1.66 :s, 9H;
:CH3)3C), 1.62 :s, 9H; :CH3)3C), 1.59 :s, 9H; :CH3)3C), 1.44
:s, 9H; :CH3)3C); 13C NMR :CDCl3, 408C) d 146.53,
139.63, 138.93, 133.75, 132.14, 130.24, 129.57, 128.70,
128.58, 128.02, 127.44, 127.39, 126.90, 124.82, 123.85,
122.65, 122.44, 122.33, 120.41, 120.13, 38.39, 38.21,
35.66, 34.93, 34.56, 34.36, 32.82, 31.78, 19.60. Anal.
Calcd for C47H51Br: C, 81.13; H, 7.39. Found: C, 81.12;
H, 7.11.
1
132.58C; HNMR d 8.63 :d, Jˆ1.6 Hz, 2H; H-4,5), 8.19
:s, 2H; H-9,10), 7.98 :d, Jˆ1.6 Hz, 2H; H-2,7), 1.49 :s, 18H;
:CH3)3C); 13C NMR d 150.75, 131.71, 130.12, 129.02,
126.30, 124.15, 118.47, 35.74, 31.75. Anal. Calcd for
C22H24Br2: C, 58.95; H, 5.40. Found: C, 59.12; H, 5.26.
4.1.13. 3,6-Di-tert-butylphenanthrene-1,8-dicarboxalde-
hyde 115). A procedure similar to that described above for
aldehyde 4 was followed. Starting from 4.63 g :10.3 mmol)
of dibromophenanthrene 14, 50 mL of anhydrous ether,
19 mL :30 mmol) of a 1.6 M solution of n-BuLi in hexanes,
and 2.92 g :40 mmol) of DMF there was obtained, after
recrystallization of the crude product from a mixture of
hexanes and toluene, 2.17 g :61%) of 15 as white crystals:
mp 188.0±190.58C; 1HNMR d 10.58 :s, 2H; CHO), 9.20 :s,
2H; H-9,10), 9.00 :d, Jˆ1.9 Hz, 2H; H-4,5), 8.23 :d,
A crystal of 11 suitable for single crystal X-ray analysis was
grown from 1-methylnaphthalene solution by slow evapora-
tion at 1508C under a stream of argon.
4.1.10. 2-Bromo-4-tert-butylbenzaldehyde 112). A solu-
tion was prepared from 22.1 mL of a 21% w/w solution of
sodium ethoxide in absolute ethanol :68 mmol of NaOEt)
and 225 mL of absolute ethanol. To this solution was
added, under nitrogen, 6.1 mL :68 mmol) of 2-nitropropane
followed by 19 g :62 mmol) of neat 2-bromo-4-tert-butyl-
benzyl bromide :2). The reaction mixture was stirred
magnetically for 4 h at room temperature, and then it was
®ltered to remove sodium bromide. The ®ltrate was rotary
evaporated and the residue was dissolved in ether and
washed sequentially with water, 10% aqueous sodium
hydroxide, and brine. Rotary evaporation of the ether
layer and molecular distillation of the red residue under
reduced pressure :0.01 mm Hg) gave 13.1 g :88%) of 12
Jˆ1.9 Hz, 2H; H-2,7), 1.57 :s, 18H; :CH3) C); 13C NMR
3
d 193.61, 149.14, 133.86, 131.69, 130.59, 128.56, 124.82,
124.42, 35.49, 31.49. Anal. Calcd for C24H26O2: C, 83.20;
H, 7.56. Found: C, 83.09; H, 7.46.
4.1.14. 1E,E)-1,8-bis-18-Bromo-4,6-di-tert-butyl-1-phenan-
thrylvinyl)-3,6-di-tert-butylphenanthrene 116). A Wittig
procedure similar to that described above for stilbene 10
was carried out starting with 0.081 g :1.54 mmol, 60%
dispersed in mineral oil) of NaH, 20 mL of DMSO, 0.92 g
:1.28 mmol) of phosphonium salt 8, and 0.21 g :0.61 mmol)

3722
F. B. Mallory et al. / Tetrahedron 57 *2001) 3715±3724
of dialdehyde 15. The reaction was allowed to proceed over-
night at 808C. The crude Wittig product was dissolved in
benzene containing a crystal of iodine, and the magnetically
stirred solution was irradiated with visible light for 3 d to
effect Z-to-E isomerization. The resulting product was
recrystallized from a mixture of toluene and 95% ethanol
to give 0.38 g :58%) of 16 as a white powder: mp 285±
2878C; 1HNMR d 8.77 :br s, 2H; H-4,5), 8.25 :d,
Jˆ1.4 Hz, 2H; H-50,500), 8.14 :s, 2H; H-9,10), 8.10 :A of
AB q, Jˆ9.3 Hz, 2H; H-90,900 or H-100,1000), 8.05 :B of AB
q, Jˆ9.3 Hz, 2H; H-100,1000 or H-90,900), 8.00 :br s, 2H; H-
2,7), 7.97 :A of AB q, Jˆ15.7 Hz, 2H; alkenyl H), 7.84 :B
of AB q, Jˆ15.7 Hz, 2H; alkenyl H), 7.95 :A of AB q,
Jˆ8.0 Hz, 2H; H-20,200 or H-30,300), 7.88 :B of AB q,
Jˆ8.0 Hz, 2H; H-30,300 and H-20,200), 7.85 :d, Jˆ1.8 Hz,
2H; H-70,700), 1.60 :s, 18H; :CH3)3C), 1.57 :s, 18H;
:CH3)3C), 1.44 :s, 18H; :CH3)3C); 13C NMR d 149.07,
148.64, 146.15, 135.75, 133.06, 132.87, 131.26, 130.60,
129.25, 129.16, 128.97, 128.84, 128.48, 128.44, 128.04,
125.51, 124.04, 122.22, 121.91, 38.51, 35.55, 35.49,
34.40, 31.81, 31.65. Anal. Calcd for C70H76Br2: C, 78.05;
H, 7.11. Found: C, 77.86; H, 7.18.
H-3 or H-2), 7.89 :d, Jˆ1.7 Hz, 1H; H-7); 1.53 :s, 9H;
:CH3)3C), 1.43 :s, 9H; :CH3)3C); 13C NMR d 192.90,
156.65, 146.86, 133.40, 132.27, 132.22, 129.74, 129.24,
128.80, 128.64, 128.41, 127.57, 123.14, 122.32, 122.25,
39.68, 35.71, 34.37, 31.76. Anal. Calcd for C23H25BrO: C,
69.52; H, 6.34. Found: C, 69.70; H, 6.25.
4.1.17. 1E)-1,2-Di-18-bromo-4,6-di-tert-butyl-1-phenan-
thryl)ethene 119). The addition by syringe of 2.8 mL
:25 mmol) of titanium tetrachloride to 40 mL of magneti-
cally stirred anhydrous THF maintained at 08C under nitro-
gen gave an opaque yellow slurry. After 20 min, 3.14 g
:48 mmol) of zinc dust was added, and the reaction mixture
turned blue-gray. A solution of 9.25 g :24 mmol) of alde-
hyde 18 in 30 mL of anhydrous THF was added by cannula,
and the reaction mixture was heated and maintained at
re¯ux for 8 h. The reaction was quenched by the addition
of dilute aqueous hydrochloric acid, and then was extracted
three times with toluene. The toluene extract was washed
with water, dried over sodium sulfate, and ®ltered. Rotary
evaporation of the ®ltrate and recrystallization of the residue
from a mixture of toluene and 95% ethanol gave 6.9 g :78%)
1
of stilbene 19 as a bright yellow solid: mp 283±2868C; H
4.1.15. 4,15-Dibromo-2,17,19,21,24,26-hexa-tert-butyl[11]
phenacene 117) from double photocyclization of 16. A
solution of 1.14 g :1.1 mmol) of 16 and 0.80 g :3.1 mmol)
of iodine in 1100 mL of cyclohexane was irradiated
:Rayonet) for 73 h at ca. 208C. The solution was concen-
trated to about 200 mL by rotary evaporation. The precipi-
tated product was collected by ®ltration and rinsed with
hexanes to give 0.49 g :43%) of 17 as a yellow solid. A
small amount of this solid was recrystallized twice from
o-dichlorobenzene to give an analytical sample of 17: mp
NMR d 8.17 :d, Jˆ1.4 Hz, 2H; H-5,50), 7.99 :A of AB q,
Jˆ9.3 Hz, 2H; H-9,90 or H-10,100), 7.95 :B of AB q,
Jˆ9.3 Hz, 2H; H-10,100 or H-9,90), 7.85 :A of AB q,
Jˆ8.1 Hz, 2H; H-2,20 or H-3,30), 7.75 :B of AB q,
Jˆ8.1 Hz, 2H; H-3,30 or H-2,20), 7.77 :d, Jˆ1.7 Hz, 2H;
H-7,70), 7.75 :s, 2H; H-a,a0), 1.49 :s, 18H; :CH3)3C), 1.36
:s, 18H; :CH3)3C); 13C NMR d 148.90, 146.36, 133.11,
133.05, 132.31, 131.42, 129.34, 129.05, 128.67, 124.48,
124.13, 124.07, 122.10, 38.70, 35.68, 34.58, 31.83. Anal.
Calcd for C46H50Br2: C, 72.44; H, 6.61. Found: C, 72.53; H,
6.69.
1
.3358C :dec); HNMR :1,4-dichlorobenzene- d4, 808C) d
9.31 :s, 2H; H-9,10 or H-22,23), 8.93 :s, 2H; H-22,23 or H-
9,10), 8.86 :A of AB q, Jˆ9.3 Hz, 2H; H-7,12 or H-8,11),
8.70 :B of AB q, Jˆ9.3 Hz, 2H; H-8,11 or H-7,12), 8.78 :s,
2H; H-20,25), 8.71 :d, Jˆ9.5 Hz, 2H; H-6,13), 8.54 :br s,
2H; H-1,18), 8.32 :d, Jˆ9.7 Hz, 2H; H-5,14), 7.93 :d,
Jˆ1.8 Hz, 2H; H-3,16), 1.83 :s, 9H; :CH3)3C), 1.60 :s,
9H; :CH3)3C), 1.46 :s, 9H; :CH3)3C). Anal. Calcd for
C70H72Br2: C, 78.35; H, 6.76. Found: C, 78.41; H, 6.66.
4.1.18. 4,11-Dibromo-2,13,15,18-tetra-tert-butyl[7]phena-
cene 120). A solution of 1.20 g :1.6 mmol) of stilbene 19
and 0.4 g :1.6 mmol) of iodine in 50 mL of toluene and
500 mL of hexanes was irradiated :Rayonet) for 2.5 d.
The precipitated product was collected by ®ltration and
rinsed with hexanes to give 0.98 g :82%) of 20 as a yellow
1
solid: mp 3208C :dec); HNMR d 8.99 :s, 2H; H-7,8 or
H-16,17), 8.68 :s, 2H; H-16,17 or H-7,8), 8.66 :d, Jˆ9.2 Hz,
2H; H-6,9), 8.31 :br s, 2H; H-1,14), 8.24 :d, Jˆ9.2 Hz, 2H;
H-5,10), 7.77 :d, Jˆ1.7 Hz, 2H; H-3,12), 1.48 :s, 18H;
:CH3)3C), 1.41 :s, 18H; :CH3)3C); 13C NMR :458C) d
146.58, 146.35, 133.23, 130.67, 130.49, 129.39, 128.85,
128.71, 128.23, 127.33, 125.29, 125.07, 122.60, 122.37,
121.67, 39.08, 35.72, 35.11, 31.81. Anal. Calcd for
C46H48Br2: C, 72.63; H, 6.36. Found: C, 72.45; H, 6.50.
4.1.16. 8-Bromo-4,6-di-tert-butylphenanthrene-1-carbox-
aldehyde 118). To a magnetically stirred solution prepared
from 8.2 mL of a 21% w/w solution of sodium ethoxide
in absolute ethanol :25 mmol of NaOEt) and 70 mL of
absolute ethanol was added, under nitrogen, 2.3 mL
:25 mmol) of 2-nitropropane followed by a solution of
10.6 g :22.9 mmol) of benzylic bromide 7 in 40 mL of ben-
zene. The mixture was stirred for 24 h at room temperature,
and then was ®ltered to remove sodium bromide. The ®ltrate
was rotary evaporated, and the residue was dissolved in
toluene and washed sequentially with water, 10% aqueous
sodium hydroxide, and brine. The organic layer was dried
over sodium sulfate and ®ltered. The ®ltrate was passed
through a short pad of silica gel. Then the toluene was
removed, initially using a rotary evaporator and then using
a vacuum pump, to give 9.05 g :99%) of aldehyde 18 as a
4.1.19. 1E)-1-18-bromo-4,6-di-tert-butyl-1-phenanthryl)-
2-150-tert-butyl-20-methylphenyl)ethene 121). The addi-
tion of 4.1 mL :8.2 mmol) of a 2.0 M solution of n-BuLi
in pentane to a solution of 1.6 mL :11.0 mmol) of diisopro-
pylamine in 25 mL of THF was followed by the addition of
a solution of 5.92 g :8.2 mmol) of phosphonium salt 8 in
100 mL of THF. The reaction mixture turned red. A solution
of 1.31 g :7.4 mmol) of aldehyde 4 in 20 mL of THF was
added, and the mixture was heated under re¯ux overnight.
The cooled reaction mixture was poured into aqueous am-
monium chloride. The resulting mixture was extracted with
toluene and the toluene extract was washed with brine and
1
yellow solid: mp 119±1228C; HNMR d 10.43 :s, 1H;
CHO), 9.02 :d, Jˆ9.4 Hz, 1H; H-10), 8.19 :d, Jˆ9.4 Hz,
1H; H-9), 8.15 :d, Jˆ1.6 Hz, 1H; H-5), 8.03 :A of AB q,
Jˆ7.9 Hz, 1H; H-2 or H-3), 7.96 :B of AB q, Jˆ7.9 Hz, 1H;

F. B. Mallory et al. / Tetrahedron 57 *2001) 3715±3724
3723
rotary evaporated. The residue was dissolved in benzene, a
crystal of iodine was added, and the magnetically stirred
solution was irradiated with visible light for 5 d, after
which it was washed with aqueous sodium thiosulfate.
The organic layer was rotary evaporated and the residue
was treated with hexanes. The insoluble material was
removed by ®ltration and the ®ltrate was rotary evaporated.
The residue was recrystallized from acetonitrile to give
2.86 g :64%) of 21 as white crystals. A small sample was
recrystallized to constant mp from a mixture of toluene and
95% ethanol: mp 180±1828C; 1HNMR d 8.23 :d,
Jˆ1.8 Hz, 1H; H-5), 8.03 :s, 2H; H-9,10), 7.89 :A of AB
q, Jˆ8.1 Hz, 1H; H-2 or H-3), 7.73 :B of AB q, Jˆ8.1 Hz,
1H; H-3 or H-2), 7.84 :d, Jˆ1.8 Hz, 1H; H-7), 7.69 :d,
Jˆ2.2 Hz, 1H; H-60), 7.65 :d, Jˆ15.8 Hz, 1H; H-a), 7.35
:d, Jˆ15.8 Hz, 1H; H-a0), 7.28 :dd, Jˆ8.0, 2.0 Hz, 1H;
H-40), 7.16 :d, Jˆ8.0 Hz, 1H; H-30), 2.42 :s, 3H; ring
CH3), 1.55 :s, 9H; :CH3)3C), 1.43 :s, 9H; :CH3)3C), 1.39
:s, 9H; :CH3)3C); 13C NMR d 149.32, 148.39, 146.10,
136.42, 133.29, 133.23, 131.00, 130.47, 129.14, 129.09,
128.80, 128.45, 127.01, 125.19, 124.18, 123.93, 122.72,
38.44, 35.47, 34.71, 34.37, 31.66, 31.64, 19.72. Anal.
Calcd for C35H41Br: C, 77.62; H, 7.63. Found: C, 77.86;
H, 7.48.
13C NMR :458C) d 150.45, 146.65, 139.29, 133.96, 133.02,
132.88, 131.68, 131.00, 130.22, 129.37, 129.02, 128.85,
128.17, 127.56, 127.36, 125.00, 122.98, 122.65, 122.48,
121.16, 38.75, 38.54, 35.79, 35.86, 34.34, 32.51, 31.89.
Anal. Calcd for C35H38Br2: C, 67.97; H, 6.19. Found: C,
68.06; H, 6.31.
4.1.22.
9-Bromo-1,11,13-tri-tert-butyl[5]phenacene-4-
carboxaldehyde 124). A procedure similar to that described
above for aldehyde 18 was followed. The crude product
obtained from reaction of 0.49 mL of a 21% w/w solution
of sodium ethoxide in anhydrous ethanol :1.5 mmol of
NaOEt), 10 mL of anhydrous ethanol, 0.14 mL :1.5 mmol)
of 2-nitropropane, and a solution of 0.87 g :1.4 mmol) of
benzylic bromide 23 in 40 mL of benzene was dissolved in
toluene and washed sequentially with water, 10% aqueous
sodium hydroxide, and brine. The organic layer was dried
over sodium sulfate and ®ltered. The ®ltrate was rotary
evaporated, and the residue was recrystallized from a
mixture of toluene and 95% ethanol to give 0.42 g :54%)
of aldehyde 24 as a yellow solid: mp 224±2278C; 1HNMR
d 10.49 :s, 1H; CHO), 9.27 :d, Jˆ9.3 Hz, 1H; H-5),
8.71±8.68 :m, 2H; H-6 and H-7), 8.61 :s, 1H; H-14), 8.42
:br s, 1H; H-12), 8.32 :d, Jˆ9.1 Hz, 1H; H-8), 8.09 :A of
AB q, Jˆ7.9 Hz, 1H; H-2 or H-3), 8.03 :B of AB q,
Jˆ7.9 Hz, 1H; H-3 or H-2), 7.92 :d, Jˆ1.7 Hz, 1H;
H-10), 1.59 :s, 9H; :CH3)3C), 1.52 :s, 9H; :CH3)3C), 1.49
:s, 9H; :CH3)3C); 13C NMR d 193.27, 156.57, 146.76,
139.64, 133.98, 133.74, 132.81, 132.59, 131.39, 129.52,
129.45, 129.19, 129.14, 129.06, 128.58, 128.12, 127.30,
125.28, 123.47, 123.02, 122.57, 39.51, 38.59, 35.80,
34.69, 34.34, 31.88. Anal. Calcd for C35H37BrO: C, 75.94;
H6.74. Found: C, 75.84; H, 6.63.
4.1.20. 9-Bromo-1,11,13-tri-tert-butyl-4-methyl[5]phena-
cene 122). A solution of 1.50 g :3.3 mmol) of stilbene 21
and 0.8 g :3.1 mmol) of iodine in 1 L of cyclohexane was
irradiated :Rayonet) for 48 h. The reaction mixture was
washed with aqueous sodium bisul®te and water, and the
organic layer was rotary evaporated. The residue was
recrystallized from a mixture of 95% ethanol and hexanes
to give 0.89 g :50%) of 22 as a pale yellow solid: mp 246.5±
248.08C; 1HNMR d 8.70 :s, 1H; H-14), 8.68 :d, Jˆ9.3 Hz,
1H; H-7), 8.48 :d, Jˆ9.3 Hz, 2H; H-6), 8.42 :br s, 1H;
H-12), 8.27 :d, Jˆ9.2 Hz, 1H; H-8), 8.03 :d, Jˆ9.2 Hz,
1H; H-5), 7.90 :d, Jˆ1.6 Hz, 1H; H-10), 7.83 :d,
Jˆ7.8 Hz, 1H; H-2), 7.40 :d, Jˆ7.7 Hz, 1H; H-3), 2.74 :s,
3H; ring CH3), 1.59 :s, 9H; :CH3)3C), 1.51 :s, 9H; :CH3)3C),
1.49 :s, 9H; :CH3)3C); 13C NMR d 146.41, 146.32, 138.65,
133.95, 132.49, 132.10, 130.16, 129.10, 128.64, 128.57,
128.00, 126.92, 124.52, 123.80, 122.59, 119.87, 38.27,
38.08, 35.58, 34.84, 34.17, 31.71, 19.71. Anal. Calcd for
C35H39Br: C, 77.91; H, 7.28. Found: C, 78.16; H, 7.07.
4.1.23. 1E)-1,2-Di-4-19-bromo-1,11,13-tri-tert-butyl[5]
phenacenyl)ethene 125). A procedure similar to that
described above for diarylethylene 19 was followed. The
crude product obtained starting from 0.085 mL :0.77 mmol)
of titanium tetrachloride, 0.095 g :1.46 mmol) of Zn dust, and
0.406 g :0.73 mmol) of aldehyde 24 was recrystallized from
a mixture of toluene and 95% ethanol to give 0.17 g :44%)
of diarylethylene 25 as a bright yellow solid that did not
melt below 3508C: 1HNMR d 8.72 :s, 2H; H-14,140), 8.70
:d, Jˆ9.1 Hz, 2H; H-6,60 or H-7,70), 8.53 :d, Jˆ9.3 Hz, 2H;
H-7,70 or H-6,60), 8.44 :br s, 2H; H-12,120), 8.32 :d,
Jˆ9.3 Hz, 2H; H-5,50 or H-8,80), 8.29 :d, Jˆ9.1 Hz, 2H;
H-8,80 or H-5,50), 8.03 :A of AB q, Jˆ8.1 Hz, 2H; H-2,20
or H-3,30), 7.95 :B of AB q, Jˆ8.1 Hz, 2H; H-3,30 or
H-2,20), 8.01 :s, 2H; H-a,a0), 7.91 :d, Jˆ1.3 Hz, 2H;
H-10,100), 1.64 :s, 18H; :CH3)3C), 1.55 :s, 18H;
:CH3)3C), 1.50 :s, 18H; :CH3)3C); 13C NMR d 148.76,
146.69, 139.31, 133.62, 133.11, 132.66, 131.11, 130.34,
129.74, 129.43, 129.35, 129.06, 128.14, 127.37, 124.85,
123.79, 122.50, 120.45, 38.53, 38.47, 35.72, 34.94, 34.36,
31.84. Anal. Calcd for C70H74Br2: C, 78.20; H, 6.94. Found:
C, 78.41; H, 6.90.
4.1.21. 9-Bromo-4-bromomethyl-1,11,13-tri-tert-butyl[5]
phenacene 123). A procedure similar to that described
above for benzylic bromide 2 was followed. A mixture of
0.46 g :2.6 mmol) of N-bromosuccinimide, 1.40 g
:2.6 mmol) of methyl[5]phenacene 22, a pinch of benzoyl
peroxide, and 25 mL of carbon tetrachloride was heated
under re¯ux for 24 h. The reaction mixture was cooled
and ®ltered to remove succinimide. A small amount of silica
gel was added to the ®ltrate, the mixture was ®ltered, and the
resulting ®ltrate was rotary evaporated. Recrystallization of
the residue from acetonitrile yielded 1.41 g :87%) of
1
benzylic bromide 23 as a yellow solid: mp 145±1508C; H
NMR d 8.70 :d, Jˆ9.4 Hz, 1H; H-7), 8.65 :s, 1H; H-14),
8.62 :d, Jˆ9.2 Hz, 1H; H-6), 8.42 :d, Jˆ1.1 Hz, 1H; H-12),
8.29 :d, Jˆ9.2 Hz, 1H; H-8), 8.19 :d, Jˆ9.2 Hz, 1H; H-5),
7.91 :d, Jˆ1.7 Hz, 1H; H-10), 7.87 :d, Jˆ7.9 Hz, 1H; H-2),
7.60 :d, Jˆ7.9 Hz, 1H; H-3), 5.04 :s, 2H; CH2Br), 1.58 :s,
9H; :CH3)3C), 1.52 :s, 9H; :CH3)3C), 1.49 :s, 9H; :CH3)3C);
4.1.24. 4,15-Dibromo-2,17,19,21,24,26-hexa-tert-butyl[11]
phenacene 117) from photocyclization of diarylethylene
25. A solution of 150 mg :0.14 mmol) of 25 and 230 mg
:0.91 mmol) of iodine in 50 mL of toluene and 300 mL of
hexanes was irradiated :Rayonet) for 27 h. The solution
was ®ltered and the precipitated product was collected by

3724
F. B. Mallory et al. / Tetrahedron 57 *2001) 3715±3724
®ltration and rinsed with hexanes to give 87 mg of 17 as a
yellow solid that did not melt below 3508C. Based on the
recovery of 30 mg of starting material 25 from the ®ltrate,
the 87 mg of product that was obtained represents a 73%
References
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Tetrahedron Lett. 1996, 37, 7173±7176.
1
yield of 17: HNMR :1,4-dichlorobenzene- d4, 1008C) d
2. Mallory, F. B.; Butler, K. E.; Evans, A. C.; Brondyke, E. J.;
Mallory, C. W.; Yang, C.; Ellenstein, A. J. Am. Chem. Soc.
1997, 119, 2119±2124.
9.31 :s, 2H; H-9,10 or H-22,23), 8.93 :s, 2H; H-22,23 or
H-9,10), 8.86 :A of AB q, Jˆ9.3 Hz, 2H; H-7,12 or H-8,11),
8.70 :B of AB q, Jˆ9.3 Hz, 2H; H-8,11 or H-7,12), 8.78 :s,
2H; H-20,25), 8.71 :d, Jˆ9.5 Hz, 2H; H-6,13), 8.54 :br s,
2H; H-1,18), 8.32 :d, Jˆ9.1 Hz, 2H; H-5,14), 7.92 :br s, 2H;
H-3,16), 1.82 :s, 18H; :CH3)3C), 1.59 :s, 18H; :CH3)3C),
1.46 :s, 18H; :CH3)3C).
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Acknowledgements
Acknowledgement is made to the donors of The
Petroleum Research Fund, administered by the American
Chemical Society, for partial support of this research
through Grant 32796-AC1. We are grateful to the National
Institutes of Health for partial support of this work
through Academic Research Enhancement Award 1 R15
GM57647-01.
5. Stock, L. M.; Brown, H. C. J. Am. Chem. Soc. 1959, 81, 5615±
5620.